The present invention relates to joining tubes to a tube sheet and, in particular, to explosive expansion of the tubes within tube holes.
The concept of expanding tubes in tube sheets is not new. For low pressure use, tubes have been mechanically expanded within tube sheet holes and frequently this is all that is needed to hold the tubes within the tube sheet. Frequently, circular or longitudinal grooves are made in the wall of the holes and the tubes are expanded into the grooves to obtain a more effective grip on the tubes. In high pressure work, it is customary to weld the tube ends to the tube sheet, and then expand the tubes in the area of overlap between the tubes and tube sheet, for the purpose of avoiding crevices in which corrosive materials can lodge.
It is also known to expand a tube within a tube sheet by employing a cylindrical, polyethylene insert having an axial bore filled with an explosive charge (U.S. Pat. No. 3,411,198). This insert is placed inside a tube positioned within a tube sheet, the outside of the insert being surrounded by a buffering sleeve also of polyethylene. The foregoing expansion technique has been found to operate satisfactorily for tube sheets which are many times thicker than the diameter of the tube being joined to the sheet. This known technique takes advantage of the relatively long piece of tube contained within the sheet to develop a tapering effect. Specifically, the amount of expansion occurring at either end of the polyethylene insert is lessened since the material of the insert has a propensity to extrude axially at its ends.
It is also known to join sections of pipe by inserting them into a connecting sleeve encircling the joint. A turn of detonating cord is wrapped around each end of the connecting sleeve and detonated to swage inwardly the sleeve and bind it to the two sections of pipe. However, this technique basically does not concern outwardly directed, radial deformation as is required to join a tube to a tube sheet. Furthermore, this known technique fails to include a buffer for transmitting energy and protecting the work-pieces from damage.
Still another explosive expansion technique is shown in U.S. Pat. No. 3,543,370.
Accordingly, there is need for an efficient apparatus and method for joining tubes to a tube sheet through an explosive expansion. This technique ought to be suitable for joining large diameter tubes to a relatively thin tube sheet.